A number of processes have been developed for heating food. For example, it is common knowledge that food can be cooked or otherwise heated in an oven, or a range or over a fire. Although different implements are used in each of these processes, e.g. the food may be placed within a pot or mounted on a spit, almost all of these heating or cooking processes share the common denominator of a high temperature heat source. Thus, in the case of a gas fired oven or range, an open flame is the source of heat and in the case of an electric range, oven or broiler, a high temperature, electrically heated element supplies the required heat. Indeed, in the case of an electrically heated oven the heating element may be incandescent.
The use of a high temperature heat source in conventional cooking processes is necessitated by the heat transfer mechanisms which are relied upon. For example, when foods are broiled there is no physical contact between the heat source and the food. Thus, it is commonly believed that the prevailing heat transfer mechanism is radiation and since radiant heat transfer increases with the fourth power of the absolute temperature of the heat source, high temperature heat sources such as an open flame or an incandescent tube are employed.
Similarly, when foods are fried or otherwise heated in a thick pan or pot, the prevailing heat transfer mechanism within the pot is conduction. Thus, heat must be conducted through the pot or pan and then transferred by conduction from the pan surface to the food. In order for heat to be transferred by conduction, through the pan and then to the food, a high temperature difference must exist between the external heat source and the food. Therefore, resort was made to an open flame or a high temperature, electrically heated element.
Traditional prior art cooking processes, e.g. roasting, broiling and frying, employed a high temperature heat source. The efficiency of such processes is generally very poor, i.e. a substantial quantity of heat must be generated in order to transfer a small portion of such heat to the food or article to be cooked or heated. In the case of radiant heat transfer, such low efficiency arises because a high temperature heat source will radiate heat in all directions. Thus, with an open flame or electrical element heating a pot or broiling a food, heat will be radiated in all directions and only a portion of the radiated heat from the flame or electrical element will be transferred to the pot or food article to be heated. Therefore, a substantial quantity of the heat generated by an open flame or electrical heater will heat the air and thereby be lost.
In the case of frying or heating foods in a pan or pot, other sources of inefficiencies are inherently present. For example, it is obvious that in such processes the heavy pan or pot itself must be heated. Thus, a portion of the cooking heat generated will not be used for cooking but will, instead, be used to heat the heavy container in which the food is located.
The inefficiencies which attend the practice of heating processes wherein a pot or pan is used were recognized by prior art workers and efforts were made to minimize such inefficiencies by expedients such a fabricating thick pots from materials which had a high thermal conductivity, e.g. aluminum. Although these expedients reduced (but did not eliminate) some of the inefficiencies heretofore mentioned, there are still other sources of inefficiency which could not be avoided. For example, anytime a high temperature heat source is employed, the entire surroundings are heated and the heating efficiency of the process is poor.
An inefficiency which attends the practice of broiling and which is essentially unavoidable results from the fact that substantially the same amount of heat is generated in a given size apparatus irrespective of the quantity of food which is cooked. Thus, if one cooks a single hamburger or six hamburgers in a broiler, because of the indiscriminate heat generation substantially the same amount of heat will be generated in either case. As a result, when only one or two small articles are broiled, the efficiency in terms of the amount of heat generated per pound of food cooked is exceedingly low.
In addition, it is known that as a result of broiling or frying there are utensils which must be cleaned. Thus, both the oven and the food container must be cleaned after food is heated or cooked.
In summary, it will be appreciated that the domestic practice of traditional food cooking processes, such as broiling, roasting and heating foods in a pot or pan, are characterized by low efficiencies and undesirable side effects in the nature of overheating the cooking environment and producing utensils which must be cleaned.
In addition to traditional domestic cooking processes, the prior art also discloses a number of other cooking processes.
For example, a recently developed cooking process employs microwaves to heat food. Although microwave cooking overcomes some of the disadvantages of traditional prior art cooking processes, certain other disadvantages are still present. For example, the conversion efficiency from A.C. power to microwaves is only approximately 50%. Additionally, since microwave devices operate by generating heat within the food surface rather than transferring from a high temperature source, the outer surface of a food cooked in a microwave oven may lack the browned appearance which most people have come to associate with certain cooked foods, e.g. steaks or hamburgers. In addition, microwave ovens are particularly expensive and their design and operating characteristics are such that certain safety problems are presented requiring radiation shielding.
Another prior art food heating process is exemplified by the disclosures of U.S. Pat. Nos. 3,361,054, 2,648,275, 2,474,390, 2,059,133, 1,990,412, 1,915,962, 1,902,564, 1,882,363, 1,802,532. In the process disclosed in these patents, an elongated food article, e.g. a frankfurter or potatoe, is mounted on a metal pin which contains a high temperature electrical heater. Thus, it will be seen that this process, like traditional processes, resorts to the use of a high temperature heat source to heat a food which is isolated from the heat source. Therefore, heat must be transferred from the heating element through the metal pin and the pin itself must be heated before heating of the food commences. In addition, any device for practicing such a process has only very limited utility.
Another food heating process suggested by the prior art is disclosed in U.S. Pat. Nos. 267,684, 2,939,793, 2,896,527, 2,226,036, 2,222,087. In accordance with the process disclosed in these patents, a food is heated by passing an electric current directly through the food. In the practice of this process it is often necessary to specially prepare the food article so as to enhance its conductivity or provide a surface which can be appropriately connected to an electrode. In addition to the disadvantage of often requiring specific preparation of the food, the practice of this process, like microwave cooking, apparently did not provide a desired browning of the food, so it was proposed (see U.S. Pat. No. 2,226,036) to include a high temperature radiant heating device to heat and brown the outside of the food. Of course, the utilization of any such radiant heating device would, as noted above, contribute substantially to whatever inefficiencies were already present in the process. Further, more recent prior art workers have noted that if a food is cooked by passing an electric current through the food, the quality of the resulting, heated food may be deleteriously affected as a result of some form of galvanic action. Additionally, it is apparent that the utility of this process, like the previously described process, is limited to a relatively small number of food articles, such as frankfurters. Possibly because of the limited utility of this process and the problems which attend the practice thereof, this process has, to my knowledge, never been widely practiced.
Some prior art workers attempted to bypass completely the traditional cooking processes and provide food articles in a package wherein the package was adapted to generate heat when appropriately connected to a suitable power source. For example, U.S. Pat. No. 3,619,214 discloses a two compartment package having a food in an upper compartment and a lower compartment containing an aqueous conductive solution such as salt water. Disposed in the lower compartment are spaced electrodes. It is asserted in the patent that when the electrodes are connected to a 120 volt power source, current will flow through the saline solution, which will thereby be heated and will boil, whereby the food in the upper compartment will be heated. It is believed evident that the complexity and cost of such a package is such as effectively to foreclose commercial utilization.
U.S. Pat. No. 3,483,358 discloses a food package which includes strip electrodes which are placed upon a film so as to form so-called meander paths. When used, the electrodes are powered by an electric potential on the order of 50 volts. Once again, it would appear that the inherent cost of such a package has precluded any wide spread use.
U.S. Pat. No. 3,751,629 includes a discussion of the difficulty of providing a food package which includes heating electrodes. Thus, it is stated in this patent that
"In practice however the conductive pattern usually cannot be allowed to come into direct contact with the substance because such contact may be undesirable for electrical reasons or on account of the nature of the substance and material of the pattern, for reasons of packaging, use or processing or storing of the substance, etc."
As a result of this view, the package disclosed in this patent includes a patterned heating element with an insulating material and a metal foil layer disposed between the heating element and the substance to be heated. The heating element is powered from a 12 volt source. Once again, the complexity and cost of this package would seem to prevent its wide spread use.
U.S. Pat. Nos. 3,210,199 to Schlaf and 3,100,711 to Eisler both disclose a food heating method and food package which may employ a metal foil, e.g. an aluminum foil. Considering first the patent to Schlaf, experiments conducted upon the occasion of my discovery have established the marginal utility of Schlaf's method and carton. More specifically, Schalf proposes an open-ended carton for packaging food articles such as frankfurters wherein the carton walls are constructed of aluminum foil having an insulating material such as cardboard laminated to the outer surface. The carton is formed so as to provide extensions of the carton wall on the same side of the food articles. The extensions are maintained in spaced apart relation by an insulator. When the carton is used to heat the frankfurters contained therein, it is proposed that the extensions are slid into clips wherein one part of each clip bears against the insulated backing and thereby urges the aluminum foil inner surface into contact with an electrical terminal. The electrical terminals may be powered from a source which provides a voltage of one volt. As a result, current will flow through the foil and it is proposed that the interior of the package is thereby heated.
The function of the laminated insulating material is to retain heat within the carton and to provide a resilient backing whereby the carton extensions may be slid into the clips. As previously stated, experiments have established the marginal utility of this package and method. For example, in Schlaf's method and construction both terminals of the power source are connected to the package along a common side thereof. Thus, from an electrical point of view, a number of problems are present. First, if any two parts of the foil should come into contact, the foil at the point or points of contact will melt. Therefore, it is absolutely critical to the practice of Schlaf's process that a spacing insulator be correctly positioned so as to separate the foil extensions of the package and, additionally, the carton must be handled with great care to insure that the walls thereof never come into physical contact. As a corollary of these constraints, it is clear that Schlaf's carton must be open ended.
Still another functional defect which arises from Schlaf's construction of connecting one side of the carton to the power source is the problem of physical support. Thus, unless some unknown means is used to rigidify the carton, the carton must be supported during the heating process lest the weight of the food articles deform the carton thereby permitting opposed walls of the carton to contact each other.
A deficiency intrinsic to Schlaf's process is the apparent reliance on convective heat transfer, i.e. Schlaf states that the heated aluminum foil will heat the interior of the carton. Therefore, it appears that Schlaf is relying upon radiation and convection to transfer heat from the foil to the food. With respect to radiant heat transfer, it was previously pointed out that radiant heat transfer varies with the fourth power of the absolute temperature of the radiating source. Therefore, unless Schlaf's method is practiced in such a manner as to insure that the foil is at a high absolute temperature, relatively little radiant heat transfer will occur. And, militating against the use of high foil temperatures is the combustibility of the insulating laminate which, according to Schlaf, may be cardboard.
Considering convective heat transfer, it will be recalled that the nature of Schlaf's process and carton is such that the aluminum foil carton must, of necessity, be open to avoid a short circuit. Since the foil carton must be open ended, air may then circulate through the carton.
Finally, it should be noted that Schlaf's process and carton construction require the use of an insulated foil material. As such, the process and carton construction disclosed by Schlaf require a specialized construction material which must meet a variety of conflicting requirements. Possibly for this reason and in view of the inefficiencies, complexities and functional problems heretofore noted, Schlaf's process and carton construction has not been used to any known extent.
Eisler, in U.S. Pat. No. 3,100,711, discloses a food package which is similar to the carton proposed by Schlaf, i.e. Eisler proposes to position a series connected metal foil within a package containing food and power the foil with a potential of 12 to 18 volts. Eisler suggests that the foil may be patterned to achieve an appropriate resistance and may be mounted on a plastic foil. In view of the detailed consideration heretofore presented with respect to Schlaf's method and carton and the similarities between Schlaf's and Eisler's method, it is believed sufficient simply to note these similarities and the corresponding deficiencies and functional problems shared by both processes and constructions.
Another prior art cooking process is disclosed by U.S. Pat. Nos. Hager (3,596,059), Park (2,070,491) and Clark (2,140,348). As disclosed in these patents, a pot or other form of food container is directly heated, e.g. by bombarding the pot with an electron beam or passing an electric current through the bottom of the pot. Although such approaches may overcome some of the inefficiencies of traditional prior art cooking processes, other inefficiencies and disadvantages are still present. For example, since a pot is used a certain amount of heat is expended in simply heating the pot rather than the food contained therein. Also, after the pot is heated it will then function to dissipate heat. Further, after the heating or cooking is complete, there remains the problem of cleaning the pot.
U.S. Pat. Nos. 3,771,433 and 3,669,003 to King disclose an apparatus for heating pre-cooked and pre-packaged foods. Among other things, this apparatus appears to have only limited utility and, to the best of my knowledge has never achieved any degree of commercial acceptance.
In summary, the prior art relating to my discovery includes traditional, domestic food heating and cooking processes, the practice of which is characterized by a number of inefficiencies and esthetic drawbacks. In addition to traditional cooking processes, the prior art discloses a number of arcane heating or cooking processes, none of which appear to have achieved any significant degree of commercial acceptance and all of which have limited or marginal utility.